According to what I have read, its costs about $3 to charge the battery from 0% to 100%.

The Chevy Volt claims about the same. " A. Electricity is an extremely affordable transportation fuel. With a fully charged battery, most people can commute gas- and tailpipe emissions-free for about $1.50 per day(1). That's about the same annual cost as running a common household appliance. To save even more, some utility companies offer lower electricity rates for vehicles charging during off-peak periods, such as night.

(1) EPA estimated 35 miles initial range based on 93 MPGe (electric); actual range varies with conditions."